A typical vane-type camshaft phaser for changing the phase relationship between a crankshaft and a camshaft of an internal combustion engine generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. Engine oil is selectively supplied to one of the advance and retard chambers and vacated from the other of the advance and retard chambers by a phasing oil control valve in order to rotate the rotor within the stator and thereby change the phase relationship between an engine camshaft and an engine crankshaft. Camshaft phasers also commonly include an intermediate lock pin which selectively prevents relative rotation between the rotor and the stator at a predetermined aligned position that is intermediate of a full advance and a full retard position. The intermediate lock pin is engaged and disengaged by venting oil from the intermediate lock pin and supplying pressurized oil to the intermediate lock pin respectively by a lock pin oil control valve.
Upon failure of the phasing oil control valve, it may be desirable to use the intermediate lock pin to lock the camshaft phaser at the predetermined aligned position because the predetermined aligned position may provide valve timing which allows the internal combustion engine to start and run under all conditions. Prior art camshaft phasers commonly employ a bias spring to assist in returning the camshaft phaser to the predetermined aligned position if the phasing oil control valve fails. Examples of such a bias spring are shown in U.S. Pat. No. 7,363,897 to Fischer et al. and U.S. Pat. No. 8,127,728 also to Fischer et al. While bias springs may be effective, it may be desirable to provide another arrangement in addition to or in alternative to using a bias spring to ensure engagement of the intermediate lock pin with its corresponding seat.
What is needed is camshaft phaser which minimizes or eliminates one or more the shortcomings as set forth above.